The present invention relates to a method for forming a micro-pattern on a substrate; and more, particularly, to a method for forming a micro-pattern on a substrate by employing a compression patterning technique.
One of conventional micro-pattern forming methods is a photolithography technique. In a conventional photolithography technique, since the width limit in a micro-pattern is determined by the wavelength of a light irradiated on a mask for the micro-pattern, it is difficult to fabricate a sub-100 nm structure.
Further, in a conventional process employing the photolithography technique, a process forming a pattern involves multiple steps, e.g., pattern formation, etching and cleaning step and these steps are costly and time-consuming. When the surface of a substrate on which a pattern is formed is not flat, there occurs the diffraction and/or reflection of the light, thereby rendering the process difficult to control.
To ameliorate the problem described above, there is developed a method for forming a sub-100 nm micro-pattern. An imprint process that presses a mold into a thermoplastic film on a substrate has been developed to create micro-patterns for use in various fields, e.g., integrated circuit fabrication process, photo-electric, magnetic element manufacturing process or the like. For example, a micro-pattern forming method suggested by Stephen Y. Chou et al. is described in Appl. Phys. Lett., 67(21), 20 Nov. 1995.
In this method, a mold is first pressed into a thin thermoplastic polymer film, e.g., made of polymethylmethacrylate (PMMA), on a substrate, e.g., made of silicon, the substrate being heated at a high temperature, e.g., 150 to 200xc2x0 C., higher than its glass transition temperature, e.g., 104xc2x0 C. for PMMA. Above that temperature, the polymer behaves as a viscous liquid and can flow under a pressure, thereby conforming to the mold. Then the mold is compressed against a sample and held until the temperature drops below the glass temperature. At a pressure, e.g., ranging from 100 to 150 atmospheres, the pattern on the mold can be fully transferred into the polymer film, e.g., the PMMA.
Since, however, a pressing procedure of this method is performed at a high temperature, this method cannot be performed repeatedly or repetitively. In detail, to form another pattern at another position on a substrate after forming one pattern at a certain position on the substrate, it is necessary to heat the substrate having the polymer film formed thereon again above the glass transition temperature.
But, when the substrate is heated again at the high temperature as described above, the previously formed pattern of the polymer film will disappear. Accordingly, employing the process repetitively is impossible. It should be noted that another position mention above may represent either a neighboring position of a previously patterned position or a position on top surface of the previously patterned polymer film.
To avoid this problem by performing a pressing procedure as one step, a mold should be made to have a more complex pattern, e.g., a coarse pattern coupled with a fine pattern. But in this case, there is entailed a cost problem together with a technical burden to make such a complex mold.
FIG. 5 presents a diagram showing a patterned polymer film 501 formed on a substrate 500 by using a conventional pattern forming method. When the pressing procedure is performed at a room temperature under a high pressure felt by a patterned polymer, e.g., of about 50 to 150 atmospheres, there usually occurs an undesired portion in a patterned polymer film. For example, as presented in FIG. 5, an undesired protruded portion 502 near top edges of the patterned polymer film 501 may occur due to an undesired plastic deformation thereat.
In a conventional pressing procedure, when a load is applied on a polymer film on a substrate at a room temperature, if the pressure is below a certain level, a free volume in the polymer film absorbs the pressure applied thereon by decreasing its volume. But, if the pressure is greater than a certain value, there may be resulted in a plastically deformed undesirable portion in the polymer film. It should be noted that the free volume represents total volume of voids or empty spaces in the polymer film.
In view of the foregoing, the conventional micro-pattern forming methods described above cannot form a micro-pattern having a desired pattern by performing a pressing procedure at a room temperature.
It is, therefore, a primary object of the present invention to provide a method for forming a micro-pattern on a substrate by employing a compression patterning technique at a room temperature.
In accordance with one aspect of the present invention, there is provided a micro-pattern on a substrate, the method comprising the steps of: (a) coating polymer material having a solvent on the substrate, thereby forming a polymer film on the substrate; (b) pressing a mold having a predetermined shape into the polymer film on the substrate by employing a predetermined compression technique to entail a plastic deformation of the polymer film, thereby patterning the polymer film; and (c) performing etching on the substrate through the use of the patterned polymer film as an etching mask, thereby forming a micro-pattern on the substrate.
In accordance with another aspect of the present invention, there is provided a forming a micro-pattern on a substrate, the method comprising the steps of: (a) coating polymer material having a solvent on the substrate, thereby forming a polymer film on the substrate; (b) pressing a first mold having a first predetermined shape into the polymer film on the substrate to form a first patterned polymer film and then pressing a second mold having a second predetermined shape into the first patterned polymer film by employing a predetermined compression technique, thereby providing a patterned polymer film; and (c) performing etching on the substrate through the use of the patterned polymer film as an etching mask, thereby forming a micro-pattern on the substrate.